public inbox for gcc-help@gcc.gnu.org
 help / color / mirror / Atom feed
From: "cyb_yorkin@outlook.com" <cyb_yorkin@outlook.com>
To: "gcc-help@gcc.gnu.org" <gcc-help@gcc.gnu.org>
Subject: Problem with evaluation order in assignment expression after c++17
Date: Tue, 23 Aug 2022 14:37:48 +0000	[thread overview]
Message-ID: <TYCPR01MB9385BEFA862AC062F50D3CECF3709@TYCPR01MB9385.jpnprd01.prod.outlook.com> (raw)

Hi all,

After c++17, the standard in section [expr.ass] guarantees "right operand is sequenced before the left operand".
I wrote this code, tested in gcc 12.1.

```
#include<iostream>
using namespace std;
int a = 1, b = 1;
int *ptr = &a;

int f(){
    ptr = &b;
    return 9;
}

int main(){
    *ptr = f();
    cout<<a<<','<<b<<endl;
}
```
I assume the program will evaluate function f first (it changed the ptr), and then get address of b from the pointer. After that, store returned value into b.
The output should be "1,9", like clang. but gcc give me "9,1".
You can check this here: https://godbolt.org/z/9P3cj7nYs

I wonder is that a gcc's bug or am I miss something else in c++ standard.

Thanks.


                 reply	other threads:[~2022-08-23 14:37 UTC|newest]

Thread overview: [no followups] expand[flat|nested]  mbox.gz  Atom feed

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=TYCPR01MB9385BEFA862AC062F50D3CECF3709@TYCPR01MB9385.jpnprd01.prod.outlook.com \
    --to=cyb_yorkin@outlook.com \
    --cc=gcc-help@gcc.gnu.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).